Heat treatment for centrifugally-cast pipes.



D. S. DE LAVAUD.

HEAT TREATMENT FOR CENTRIFUGALLY CAST PIPES.

APPLICATION FIL EU 1ULY30. |917 Patented Out l, |918.

2 bHEETS-SHEET l /ll/ VEN 720]? D; S. DE LAVAUD.

HEAT TREATMENT FoR cENTmFuGALLY GAST PxPEs.

APPLICATION FILED JULY 30. 1917..

1,280,418. Patentedot. 1, 1918,

2 SHEETS-SHEET 2- mab'ix v- [me y gagne/gu ferrite INVENTOR Y BY r .a"r.

" nrmr'rnr sENsAUD nernvnun, or new Yonne, n. r'.-

HEAT TREATMENT FOR CENTRIFUGALLY-CAST PIPES.

\ Application led July 30, 1917. Serial No. 183,503.

To all wh'om'z't may concern:

Be it known that I, DIMITRI SENSAUD DE -L'AVAUD, a citizen of the UnitedStates of cast under the influence of centrifugal force.

The object ofthe invention is to provide an improved heat treatment forcentrifugally cast pipes or similar articles, whereby the speed ofmanufacture of the pipe is increased, and, this latter being the mostimportant object, the quality of the pipes is bettered to a remarkabledegree.

In particular, the prime object of the pres- Speciication of LettersPatent.

ent invention is to reduce a cast iron pipe which has a very ne grain,and in which the graphite exists `in iine particles and not in coarseakes as the case is with ordinary cast iron pipes. This I accomplishrbythe follow- 4 ing steps. First, the molten metal of which ladvantageously carried out, and a typical the pipe is to be formed iissubjected to the action of centrifugal force, and at the same timerapidly cooled, the metal being preferably cooled within three 'to siXseconds after it has been poured into the mold. The casting, now ofawhite cast iron, is with. drawn from the fold immediately aftersolidification, the casting leaving the mold at substantially 15000Fahrenheit. The pipe is then superheated by elevatin its temperature tofrom '1800o to 2000 Fa renheit depending on the composition of themetal. The pipe metal changes over into gra cast iron with graphite infine particles, andy any brittlegess that vmay have been caused by thesudden cooling is removed. By this process a pipe of exceptionally linerained structure, strength and toughness 1s reduced at a comparativelyrapid rate.

he invention will be more clearly understood from the followingdescription when taken in connection with the accompanying drawingsillustrating an apparatus by which the process of the present inventionmay be molecular structure of the gray cast iron product resulting fromthe process. y

In these drawings, r

Figure 1-shows the apparatus somewhat Patented oet. il, raie.

diagrammatically and partially in section;

and

Figs. 2,. 3 and 4 are pen and ink replicas of microphotographs (450diameters) of cross sections vthrough a pipe, taken respectively nearthe outside of the and near the inside.

Referring to Fig. 1,1 is a centrifugal casting machine from which a pipe2 has been pipe, near the center drawn by the supporting carriage 3.The4 mold of this machine is preferably cooled by admitting waterthrough the'pipe 18. .Means are provided for transferring the pipe toasuperheating oven, which maybe the crane 4, suitably supported in anymanner'as from the I-beam 5. The oven may advantageously have a slopingfloor 6 resting onsuitable supports 8. The oven lis provided with a Yroof 7, preferably of refractory material Aspaced suitably from thefloor to allow of the passage of the pipes therebetween. This roof mayhave a-n arched portion'9 where the sion of combustible gases throughthe apertures 10 when they are burned within the oven. ,Thel oven isalso provided with a stack 11 which may be tted'with a damper 12 for theregulation of the draft. The stack 11 is preferably placed so that thegases ofq heating is done', which may be by the admiscontaining tar 14.The tar may be. kept in liquid conditionby burning fuel on the grate 17'A baille or guide 15 is provided for the control of the passage of thepipes through the tar pit, and the pipes as they emerge are received onthe platform 16. Y

The operation of the 'apparatus shown,

.mechanically, is briefly as follows:

Molten metal is poured into the casting machine and the pipe cast andwithdrawn from the machine in the usual manner. ,The pipe is then raisedby the crane 4, revolved ,fthrough a `right angle, and deposited uponthe upper end of the floor 6, whence it travels by its ownweight slowlydown the incline through the oven, being subjected to the 'heat of theburning gases emerging from the apertures 10. 0n emerging from the oven,

the pipes enter the tar pit 13 and are guided therethrough by the baliie15,l the Weight of the oncoming pipes being sufficient to cause thepipes to move through and out of the pit.

Thermally considered, the operation of the apparatus used in carryingout the process, is as follows:

The metal in the centrifugal casting machine 1 which is being formedinto a pipe 2 is rapidly cooled, as by Water circulation through "fthepipe 18; the casting being formed and cooled within three to six secondsafter the metal has been poured into the. machine l. The manner and rateof cooling is such that when the casting is withdrawn from the mold,immediately after solidification, the casting is at the temperature of15000 Eahrenheit. The pipe 2 is withdrawn from the machine by thetraveling` carriage 3,engaged by the crane 4, and deposited at theright-handy end of the sloping floor 6 of the oven, and passes under theroof 7 and into the zone of the burners 10, with such" celerity,preferably, that the superheating treatment of the pipe commences verysoon after the pipe is Withdrawn from the mold, that is, before the pipecools by contact with the atmosphere to a temperature appreciably lowerthan 15000 Fahrenheit. During the passage of the pipe through the oventhe temperature of \the pipe is elevated from 18000 to 20000 perhapsbetter be understood if it is ex.

Fahrenheit, depending on the composition of the metal. The process ofthe present invention will plained that iron cast in sand molds coolsvery slowly, ordinarily, its latent heat diffusing gradually. The ironbeing a liquid, it crystallizes as it approaches' the solid state, andthe essential ingredients'or impurities, so to speak, separate out andbecome entrapped or inclosed in the finally solid mass.

The principal constituent or impurity in cast iron is the carbon whichexists in the graphitic state-really pure carbon which separates out asthe iron cools. It usually exists in flakes or plates, often large-ah'Ways so if the iron cools slowly. But whether the iron cools slowly orrapidly, these Hakes or plates, that is, the lamella structure familiarto metallurgists, persists, at least to a deleterious extent. The carbonin slowly cooled iron is found in larger globules or Hakes than in ironthat cools more quickly. Thus, iron cast in a permanent metal mold,whether it revolves or not, contains smaller 'crystals of carbon as wellas of all other constituents. And when the iron, so cooled, is removedat once into the air, the cooling or accelerated formation of thecrystals is accentuated. So that one of the features of the presentinvention, or rather one of the steps of the preferred tures are largelyempirical, as is also the process, is to cool the metal rapidly as it isbeing formed into the casting in the centrifugal casting machine, sothat the pipe is formed and the casting cooled within three to sixseconds after the metalis poured into the rotating mold of the machine.The real essence of the present invention, however, is my discovery,further, that when the casting is solidified in the mold, rapidly cooledin the mold, and rapidly extracted from the mold, preferably at theinstant of solidification and when the casting is substantially at 15000Fahrenheit, the quality of the casting may be improved to a remarkableextent, as compared with any heat treatment heretofore suggested, if thecasting is superheated by elevating its temperature to from 18000 to20000 Fahrenheit depending on the composition of the metal. These lattertempera- 15000, and are therefore not4 intended to be here stated in alimiting way, but merely as illustrative of what actual experiment withvarious dierent compositions of metals have shown me. With most if notall of these compositions' of metals, the 15000 temperature has beenfound so far to be ideal at the instant of extraction of thecasting-from the mold; but in the case of the superheating temperature,this has varied, so far as noted between 18000 and 19800 Fahrenheit asthe ideal superheating temperature, depending on the composition of themetal.

When the pipe iswithdrawn', at the 15000 temperature, it has a chilledouter surface. ln certain cases, of special mixtures, the pipe ischilled throughout. It cannot be led. or drilled by tool steel, andcannot in fact be worked by any instrument whatever. YThechill consistsof cementite and pearlite, with a few black spots showing graphite. Alayer of pure pearlite may be formed at the surface. rIhe crystals areof needle formation. Near the center of the casting, that is, toward theinner wall of 11o the pipe, white dendrites of Silico-ferrite are found,surrounded by a mass of fine 4 graphite and ferrite. vSometimes thepearlis very line on the outside and inside surfaces, but a littlecoarser at the center. The absence of coarse graphite plates isnoticeable; very marked. The structure is to a certain extent similar tothat of a sand casting, but there is much less pearlite.. There 130 areWhite grains and dendries of silico-ferrite and fine graphite `and`ferrite in the matrix .of pearlite.

I olalm: 1. A process for providing improved iron annulus-type castings,which consists in providing a metal rotary mold, feeding a chargel ofmolten metal thereto'and rotating the mold to ycompress the molten metalagainst the metal mold'by centrifugal force, While congealing the moltenmetal within six seconds after pouring the metal into the mold,extracting the casting thereby formed from the mold after saidcongealing of themolten' Within six seconds after pquring the meta-linto the mold, extracting the castlng thereby formed from the mold intime to prevent the casting from losing in the mold `more heat't'han theheat Whichthe metal mold labsorbs for the congearling, and afterwardsubjecting the extractedcasting to a temperature of at least 1800oFahrenheit, and then permitting the thus superheated casting to cool. 5,

3. A process for providing -improved iron castings of the' annulus-type,which consists in providing a metal rotary mold, feed;

ing a charge of molten metal thereto and' rotating the mold to compressthe. molten metal against the metal mold by centrifugal' force,.Whilecongealing the molteny metal Within six seconds after pouring themetal into the mold, extracting the casting .thereby formed from themold at the instant when the temperature of the casting is substantially1500 Fahrenheit, then rapidly heating the extracted casting to atemperatilt ture substantially between 18000 and 2000" Fahrenheit,depending on the composition of the metal, and then permitting thecasting to cool.

4. A process for providing improved annulus-type iron castings, whichconsists in feeding a charge of molten metal to a metal rotary mold androtating the mold to compress the molten metal against the metal mold bycentrifugal force, While congealing the molten metal Within six secondsafter pouring the metal into the mold, extracting the casting therebyformed from the mold after said congealing of the molten metal asquickly as the machine permits, and after- Ward subjecting the extractedcasting to a temperature of at least substantially 500 Fahrenheit lessthan the fusion temperature of the molten metal employed, and thenpermittingthe casting to cool. v

5. A casting of gray cast-iron of the annulus-type, having a structurevery much similar to that of a sand-casting, but with very much lesspearlite; the grain being entirely normal and regular but the grainbeing very close, that is to say, very small; the absence of coarseplates of graphlte being noticeable, in fact very marked, With thegraphite Very fine on the outside and inside surfaces, but a' littlecoarser at the center; the casting being soft and easily machined 1n allparts; there `being present White grains and dendrites of Silico-ferriteand grains of line graphite and ferrite in a matrix of pearlite.

6. An iron casting of the annulus type having a molecular structurecharacterized bythe fact that the graphite is very fine on the'outsideof the casting and increases in.

coarseness a little from the outside toward. the' center of the castingbut in such manner that the outside of the casting may be easily Workedby any tool; there being present dendrites and grains'of Silico-ferriteand grains of ferrite containing tine graphite surrounded by a net Workof pearlite.

In testimony' whereof I have signed my lname to this specification.

DIMITRI SENSAUD DE LAVAUD.

